Tiling with ceramic and porcelain — the complete guide
Tiles do not fall because the adhesive was weak; they fall because the notch was too small for the tile, the adhesive skinned past its open time, or somebody deleted the joints. This guide walks from adhesive choice to grouting, with numbers you measure rather than judge by eye.
Choosing the adhesive: class before name
Read the class on the bag, not the brand name. C1 for standard ceramic indoors. C2 is higher bond for low-absorption porcelain. The T suffix means slip resistance on walls, E extended open time. S1/S2 is deformability — the deciding field over underfloor heating, on facades and with large formats: S1 deforms ≥2.5 mm, S2 over 5 mm.
The notch follows the tile
A small notch under a big tile leaves air voids — and every void is a future break point under load. The rule:
| Longest tile edge | Notch size | Note |
|---|---|---|
| Up to 10 cm (mosaic) | 4 mm | — |
| Up to 20 cm | 6 mm | — |
| Up to 40 cm | 8 mm | — |
| Up to 60 cm | 10 mm | Back-buttering recommended |
| Over 60 cm | 10–12 mm + mandatory back-buttering | S1 minimum; S2 for very thin slabs |
Mixing and open time
Water exactly as the bag states — never extra "to make it spread": excess water is a weaker adhesive and more shrinkage. Mix, let it mature 5 minutes, remix without adding water. Spread with the flat side, then comb at a steady ~60°.
Open time is the real clock on the job: only spread what you can tile within 20–30 minutes. The finger test: touch the combed bed — if nothing transfers to your finger it has skinned, and any tile placed now will grip at close to zero. Scrape the skinned bed off and spread fresh.
Coverage: lift a tile and look
Bed the tile and slide it perpendicular to the ridges with a short, firm push — that is what collapses the ridges and expels air. Then lift the first tile of every area and read its back: dry interiors are fine at 65–80% coverage; bathrooms, exteriors, underfloor heating and formats over 60 cm need 90% or more — and the only route there is double-buttering (bed + tile back).
Tile joints are not a styling choice
Tile and substrate expand and contract at different rates, and the joint is where that movement is spent. Butt-jointed tile spends it its own way: by tenting.
| Situation | Minimum width |
|---|---|
| Rectified porcelain, interior walls | 2 mm |
| General interior ceramic | 3 mm |
| Floors over underfloor heating | 3 mm |
| Exterior — facades and terraces | 5 mm |
Movement joints and the perimeter gap
Beyond tile joints there are movement joints dividing the whole field: leave a 5–8 mm perimeter gap between the last tile and the wall (the skirting hides it later) — a tile touching the wall is the first to tent. Interior fields are divided with a flexible joint every ~40 m² or 8 m run; exteriors every 3–4 m both ways. And any structural movement joint in the substrate must carry through the tiling above it — never tile across one.
Grouting and cleaning
Grout after 24 hours (check the adhesive datasheet). Rake adhesive out of the joints before it hardens — grout over hardened adhesive means a shallower joint and earlier cracking. Sponge cement haze off the face before it dries hard.
The mistakes that bring tiles down
- A 6 mm notch under a 60 cm tile — air voids the tile later cracks over.
- Spreading more bed than the open time allows, then tiling onto a dead skin.
- Butt-jointing "because the client asked" — tenting is a matter of time.
- Deleting the perimeter gap at the walls.
- Extra water in the mix to make spreading easier.
- Tiling across a structural movement joint.
Frequently asked
Is double-buttering always required?
No — in dry interiors up to 40 cm formats a well-combed bed is enough. It becomes mandatory over 60 cm, in wet areas, outdoors and over heating, because its purpose is pushing coverage past 90% and expelling air pockets.
When can the new floor take foot traffic?
Light foot traffic after 24 hours; full loading and heavy fittings after 3–7 days depending on adhesive and temperature. Cold slows the cure — do not rush it in winter.
Why is spot-fixing (dabs) banned?
Because the tile becomes a bridge over voids: it cracks under point load, the voids collect water in wet areas, and outdoors that water freezes and pops the tile. A full combed bed is the only correct method.
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Last updated: 2026-08-09